Acute poststreptococcal glomerulonephritis (APSGN) is a non-suppurative complication of group A streptoccal infections (pharyngitis or pyoderma) often seen in children. Pathogenesis involves immune complexes in the kidneys but the mechanism remains poorly defined. Streptococcus pyogenes and several species of oral streptococci produce a cationic histone-like protein (HlpA) and lipoteichoic acid (LTA) that bind, respectively, to heparan sulfate proteoglycans in basement membranes and to vascular endothelial cells of kidney tissue in vitro and in vivo. Our goal is to define the nephritogenic properties of these streptococcal components and to devise a vaccine that will protect against APSGN. Specific aims are to: 1). Define, in a rat model, the histologic and immunopathologic events induced in kidneys by the deposition of immune complexes containing HlpA or HlpA-LTA complexes. The kinetics of immunoglobulin, antigen, and complement deposition in glomeruli will be correlated with infiltration by blood- borne proinflammatory cells (monocytes, lymphocytes and neutrophils), proteinuria, and histological changes. 2). Identify epitopes of HlpA that will elicit formation of serum antibodies to block the heparan sulfate-binding site and prevent its interaction with glycosaminoglycans in glomerular capillaries. Polypeptides will be synthesized according to the known primary amino acid sequence of HlpA, linked covalently to a carrier protein and used to stimulate formation of monoclonal antibodies, which will be evaluated in a in vitro tissue- binding assay. 3). Determine the ability of neutrophils and their products (defensins) to interact with opsonized streptococci and cause release of HlpA and LTA into the environment. These experiments will monitor antigen and defensin release by degranulating phagocytes, which have engulfed streptococci in vitro, and the ability of purified defensins to induce permeability changes in viable streptococci. 4). Quantify the ability of HlpA and LTA/HlpA complexes to stimulate synthesis of cytokines (tumor necrosis factor-alpha, interleukin-l beta, interleukin-6) by human peripheral blood monocytes and umbilical vein endothelial cells in vitro. These experiments will determine whether these streptococcal components act as independent or synergistic modulins.